1. Field of the Invention
The present invention generally relates to an apparatus for improving signal-to-noise ratio and/or resolution of opto-electronic target image detection systems as well as the reliability and versatility of similar laser designator systems More specifically, the present invention adds a multi-faceted optical diverter in a system using a lens with a given aperture to focus one central beam of collimated light with a cross-section matching that aperture as it travels between a target and at least one opto-electonic device such as a laser or detector diode located at the focal point of the lens in its focal plane. The diverter includes facets that redirect similar collimated facet beams adjacent and parallel to the central beam which pass through the same lens aperture between the same target and a separate set of facet opto-electronic devices. These facet devices are located at other focal points of the lens in the same focal plane. The combination of all these beams defines a larger information relay beam. The electronic target signals in all of the beams are processed simultaneously thus providing a greatly improved information exchange. The opto-electronic devices may be light transmitters or receivers, e.g. light emitting diodes, lasers or detectors.
2. Description of the Prior Art
Automatic Target Recognition (ATR) is a desired technique for use in weapon systems to be used in the xe2x80x9cdigital battlefieldxe2x80x9d of the twenty-first century. No system now available allows for the combination of the various functions required for providing a fully functional and practical ATR system. Factors that are of importance include: detector signal to noise ratio, detector resolution, photon power projected by a laser designator on a target, and the coding of information projected by a laser designator on a target.
Most modem imaging sensors are designed to meet at least three performance lo parameters, including a minimum field of view, a minimum angular resolution, and a signal-to-noise contrast function which describes the system""s ability to discern the contrast between a target and its background. As a general rule, a sensor""s signal-to-noise ratio (SNR) can be improved by fabricating more sensitive detectors or increasing the optical aperture to collect more light. For most imaging systems, the fields of view, optical apertures, and detector sensitivities are compromises to meet hardware space requirements and to provide optimized performance under standard or most frequent conditions. In actual use, however, occasions will arise when an extra xe2x80x9cboostxe2x80x9d is needed to enhance certain aspects of image quality. In most cases the field of view and angular resolution can be modified using zoom optics or adding telescopic lenses. Enhancements to the SNR are more difficult, however, because most detectors cannot simply xe2x80x9cboostxe2x80x9d their signal levels without also increasing the noise present; and the latter is fixed by practical limits on the allowed aperture dimensions and overall design complexity. Searching techniques of prior art systems first utilize a wide field of view and then to get a better look at the target the operator switches or zooms to a narrow field of view. In imagers currently available, this puts more pixels on the target, but can result in an increased f-number and pixels that have more noise.
One method to enhance the SNR is to provide more detector elements to view the same image. This is achievable for linear scanning systems by aligning two or more identical linear arrays of detectors in parallel. The scanned image passes normally and quickly over each array of detectors, and the electronic signals from identical points in the scenery as viewed by different array detectors are then summed. This is often called xe2x80x9ctime delayed integrationxe2x80x9d (TDI), because there is a slight time delay as the image sweeps from one detector array to the next. TDI operates in synchronization with the scan rate, and is considered xe2x80x9creal-timexe2x80x9d al least for human viewing. This technique requires complex timing on the array readout, and obviously involves more complicated manufacturing processes to include the extra arrays. TDI is not practical for a two-dimensional staring array because it relies upon some method of scanning the scene.
Another technique, common to both linear array scanning and two-dimensional array staring sensor systems, involves electronically adding segments of imagery gathered from the same object or scene over time. Entire two-dimensional images are stored in an electronic frame memory, and then can be added together with specific image processing to enhance the SNR. This temporal integration can enable an increase in SNR of approximately the square-root of the number of image segments integrated. The problem with this technique is that neither the sensor nor target can be in relative motion; otherwise the shifts of object location, on the focal plane over time, will smear out image details as frames of imagery are summed over time.
Once a target is detected and identified by one system, the image of the target itself can be altered using a target designator to permit easy acquisition by much less sophisticated system. Most modern, target designators utilize at least one laser having a specific wavelength assigned for a specific target. Designators become more complex as multiple random factors and multiple targets make it harder for a weapon to acquire its intended target. The extremely short time intervals utilized for weapon execution also complicate designation. Often, it is not until an execution sequence is already in progress that the target is precisely determined. If two high cost weapon systems attack the same target, this is an unnecessary waste battlefield resources.
For imaging sensors, illumination appears to be an ideal technique, but has not yet been practically demonstrated. A popular illumination source involves sets of laser diodes or other types of illuminators. Each source requires an individual set of combining optics, which collimate a finite array of diode emitters. The larger the size of the emitter array, the greater the divergence angle of the exiting beam. This places a practical limitation on the output power that can be directed at a small target some distance away from the illuminator. The individual optics for the diodes themselves often possesses anamorphic optical powers to accommodate the varying divergences of diode output in the horizontal and vertical directions. Mismatches between the individual and combining optics often lead to additional distortion problems.
While the prior art has reported using enhancement of sensor resolution and target designation, none have established a basis for a specific apparatus and technique that is dedicated to the task of solving the particular problem addressed by applicant. Applicant provides a technique for improving sensor signal-to-noise ratio, without loss of time resolution, and in combination therewith a target designation technique, based on substantially the same optical hardware.
It is therefore one object of the invention to provide a method and apparatus for improving sensor signal to noise ratio and separately, or in combination, a similar method and apparatus for use as a target designator. According to the invention, there is disclosed an apparatus and technique for enhancement wherein several electro-optical devices, each of which represent the same pixel or group of target pixels, are mounted in the focal plane of the same collimating/de-collimating lens. A refractive or reflective non-focusing faceted diverting means is provided for folding substantially identical parallel closely spaced collimated light beams through this same lens along with the similar, parallel but un-diverted normal central beam between the target and the apparatus. Each of these beams uses the full aperture of the lens and focuses on a different electro-optical device in the focal plane of the assembly. These devices normally have optically active surfaces, such as anodes or cathodes which coincide with the foal plane, but can also communicate with the focal plane through the ends of an optical glass fiber or the like. The beams may be incoming or outgoing depending on the type of devices involved. The electro-optical devices may be diode photon detectors, light emitting diodes, laser diodes or other similar devices. The electro-optical devices preferably define at least one array on an integrated circuit chip. The chip may include both detectors and emitters on one or both sides of the chip and be rotatable to place either side in the focal plane. A central processing unit (CPU) with a power supply programs the excitation of these devices, monitors their response and stores any predetermined or new data presented on various targets.
When the electro-optical devices are light emitters, the lens assembly and faceted diverting means produce a single output beam representing the characteristics of all the emitters. The emitters can be identical resulting only in a more intense beam, e.g. in a LIDAR echo ranging system, or as a simple target designator for a weapon system. In both system the efficiency and reliability is improved by using emitters of different light wavelengths and or modulating them with codes that represent classes or specific targets and/or their most effective deterrent weapon systems.